The present invention relates to an electronic control timepiece using a power spring as a power source, and having a generator driven by the power spring and an electronic governing means operated by the electromotive force of the generator.
A conventional type of electronic control timepiece for governing speeds by using an electronic circuit with a power spring as a power source is shown in FIGS. 3 and 4. FIG. 3 is a circuit block diagram and FIG. 4 is a block diagram showing a system including such mechanism parts as a power spring, etc.
As shown in FIG. 4, timepiece hands 12 are moved and a generator 3 rotated by mechanical energy 101 stored in the power spring 1 of a timepiece via a speed increasing gear train 2. By means of the rotation of the generator 3 an electromotive force 102 is induced on both ends of a coil therein and the electromotive force 102 is temporarily stored in a smoothing capacitor 4 electrically connected to the coil as a storage power 108. An integrated circuit (hereinafter abbreviated as IC) including an oscillation circuit 7 functioning by means of a quartz oscillator 10, a frequency dividing circuit 6, a cycle comparing circuit 8, a cycle detecting circuit 9, a load control circuit 5 and the like are driven by the storage power 108. The frequency of a signal oscillated by the operation of the quartz oscillator 10 is divided to given cycles via the oscillation circuit 7 and the frequency dividing circuit 6. The divided frequency signal is outputted to the cycle comparing circuit 8 as a reference cycle signal having a cycle of, for example, 1 second.
The cycle detecting circuit 9 fetches an induced voltage 104 synchronized with the rotation cycle of the generator 3 and outputs a detected cycle signal 105 to the cycle comparing circuit 8. The cycle comparing circuit 8 compares each cycle of the reference cycle signal and the detected cycle signal, obtains a time difference between both signals and generates a cycle correction signal 106 for correcting the rotation cycle of the generator 3 and outputs it to the load control circuit 5 so as to eliminate the difference, that is, to synchronize the cycle of the generator 3 with the cycle of the reference cycle signal.
The load control circuit 5 suitably selects a load resistor by switching a switch within the circuit and thereby changes the load current of the generator 3, that is, the amount of current 107 flowing to the coil of the generator 3, and governs the speed of the rotation cycle of the generator 3 by controlling the amount of an electromagnetic brake corresponding to the amount of current. Then, it synchronizes the rotation cycle of the generator 3 with a reference cycle signal generated by the IC and the quartz oscillator 10, to make the cycle constant. Then, by making constant the moving cycle of the hands 12 linked with the speed increasing gear train 2 for driving the generator 3, chronologically precise time is maintained.
FIG. 3 shows connections among the circuits mentioned above.
Electronic control timepieces based on such a principle are described in, for example, Published Unexamined Japanese Patent Applications Nos. 59-135388 (1984) and 59-116078 (1984).
The following description relates to what is termed "duration time" in such electronic control timepieces, that is the time during which a power spring is gradually released from the state where it is wound to its limit and the hands can indicate accurate time. The duration time, as shown in FIG. 5, is determined by the release angle .theta. of the power spring where a relation between a power spring torque Tz and a minimum loss torque Thmin following the rotation of the generator becomes; EQU Tz&lt;Thmin.times.Z,
wherein Z indicates a speed increasing ratio of the gear train from the power spring to the generator.
More specifically, if the rotation cycle of the generator is t, the release angle .DELTA..theta. of the power spring per unit time is determined by; EQU 2.pi./(t.times.Z).
A value (.theta./.DELTA..theta.) obtained by dividing the release angle .theta. of the power spring by the angle .DELTA..theta. becomes duration becomes in the electronic control timepiece. Thus, the larger the speed increasing ratio Z, or the longer the rotation cycle t of the generator, the longer the duration time.
The rotation cycle t of the generator must satisfy the following conditions:
1. The rotation cycle of the generator must always be constant. Since the hands linked via the speed increasing gear train indicate time, the rotation cycle of the hands is predetermined (for example, the cycle of the second hand is one minute per one rotation). Thus, it is necessary for the generator to always rotate at a constant rotation cycle.
2. An electromotive force generated by the generator which rotates at a constant cycle must have sufficient electric power to secure stable operation of the IC and the quartz oscillator.
This is because the IC including the quartz oscillator is driven by power generated by the generator and temporarily stored in the smoothing capacitor.
3. In order to obtain sufficient electromotive force, loss of torque produced when the generator rotates must not be increased. That is, the rotation cycle of the generator coincides with a rotation cycle at a time of equilibrium between the power spring torque Tz and Th.times.z, where Th.times.z means that the sum total of loss torque such as magnetic loss torque, mechanical loss torque and the like produced by the rotation of the generator is multiplied by a speed increasing ratio Z. For this reason, when the loss of torque Th becomes; EQU Th.times.Z&gt;Tzmax
with respect to a maximum torque value Tzmax possessed by the power spring, the hand movement cycle necessary for the timepiece cannot be ensured.
The generator of an electronic control timepiece is rotated under the above three conditions relating to the rotation cycle thereof.
The following description concerns the relationship between the number of rotations of a generator and various characteristics such as the induced voltage of a coil, magnetic loss torque, mechanical loss torque and the like, referring to FIGS. 6, 7 and 8. Herein, the relationship between a rotation cycle t and the number of rotations .omega. is expressed by; EQU 1/t=.omega..
FIG. 6 is a graph showing the relationship between the number of rotations .omega. of a generator and an induced voltage E charged from the generator to the smoothing capacitor. As shown by a solid line (A) in FIG. 6, with the increase of the number of rotations of the generator, the induced voltage E increases. When the generator rotates at a number of its rotations .omega.1, the induced voltage E reaches its operational voltage El, that is, a voltage sufficient to secure the stable operation of the IC, including a quartz oscillation circuit.
FIG. 7 is a graph showing the relationship between the number of rotations .omega. of a generator and mechanical loss torque Ts. The mechanical loss torque increases with an increase in the number of rotations of a generator. The mechanical loss torque changes depending on the number of rotations of the generator and becomes Ts1 when the number of rotations is .omega.1.
FIG. 8 is a graph showing the relationship between the number of rotations of a generator and magnetical loss torque. The magnetic loss torque includes eddy-current loss torque and hysteresis loss torque. A sum of these two torque loses is the magnetic loss torque. The eddy-current loss torque increases with an increase in the number of rotations of the generator. On the other hand, the hysteresis loss torque is constant, having no relationship with the number of generator rotations, and is produced following consumption of energy made when a magnetic domain formed of a magnetic material on a magnetic path is inverted in accordance with the change of magnetic flux of a rotor magnet. The magnetic loss torque is Tu1 when the number of rotations of the generator is .omega.1.
To sum up, minimum loss torque Thmin when the generator is rotated at a number of its rotations .omega.1 is expressed by; EQU Thmin=Ts1+Tu1+Tg.
Where, Tg indicates electrical loss torque to be electrically consumed by the IC, including an oscillation circuit which is an electrical load on the generator, etc.
In the electronic control timepiece operated under the conditions mentioned above, the voltage of the smoothing capacitor is determined by a voltage induced by the generator. Thus, in the case where the operational voltage of the IC including the quartz oscillation circuit is high, it is necessary to increase the voltage induced by the generator. Conventionally, in order to increase a voltage induced by the generator, such measures as making the rotation cycle of the generator short by increasing the speed increasing ratio of the gear train, improving the magnetic characteristic of the generator, increasing the number of windings of the generator coil or the like, have generally been employed.
However, the conventional type of electronic control timepiece described above has the following problems.
If, as a first measure, the number of rotations of the generator is increased to .omega.2 and an induced voltage is increased to E2 based on the characteristic shown by a solid line (A) in FIG. 6, mechanical loss torque is also increased to Ts2 as shown in FIG. 7 and magnetic loss torque is increased to Tu2 as shown in FIG. 8. This results in the increase of the sum of these losses of torque, that is, minimum loss torque Thmin produced by the rotation of the generator.
If, as a second measure, the number of interlinking magnetic fluxes of a coil is increased by constructing the magnet included in the generator so as to make a large energy product or permeance, the characteristic shown by a broken line (B) in FIG. 6 is obtained. In this case, although an induced voltage can be increased to E2 while the number of rotations of the generator is maintained at .omega.1, magnetic loss torque also increases to Tu2 as shown by a broken line in FIG. 8. Ultimately, this results in an increase in the minimum loss torque Thmin produced by the rotation of the generator.
If, as a third measure, the number of windings of the coil is increased, the characteristic shown by the broken line (B) in FIG. 6 is again obtained and thus the induced voltage may increase. In this case, however, the length or thickness of the coil increases. Also, in the case where the coil is made long, the length of the magnetic path is increased and thus magnetic loss torque increases.
To sum up the problems:
(1) Since the minimum loss torque Thmin of the generator is increased in the first and second measures, duration time is shortened. That is, as shown in FIG. 5, when the minimum loss torque increases from Thmin1 to Thmin2, the duration time is shortened from D1 to D2.
(2) Since the space occupied by the generator is expanded in the third measure, the shape of a timepiece is large, leading to a decrease in its commercial value.
If the space occupied by the power spring is expanded so as to make the duration time longer, this also leads to a decrease in the commercial value of the timepiece.